Chem AOS2 - polymers

Polymers:

Polymers are large covalent molecules made up of monomers

*Thousands of monomers in a polymer

Plastic is not a material but a property used to describe a material’s ability to be moulded into different shapes.

Condensation Polymerisation:

monomer + monomer = polymer + H20

*Water it produced.

Condensation vs hydrolysis

Condensation - makes it

Hydrolysis - breaks it (using water to break ester or polymer)

ADDITION POLYMERISATION

Process of joining monomers together = polymerisation.

Monomer units has a hydrocarbon backbone - strong due to the covalent bonding. Weak intermolecular forces holding chains together.

Polymers joint together through the addition reaction of a double bond.

Addition polymers have the same empirical formula as their monomer units.

General Properties of Polymers:

• light and strong,

• durable,

• highly versatile and modifiable (can possess many colours and characteristics),

• flammable,

• chemically resistant (particularly against acids),

• effective thermal and electrical insulators.

LDPE VS HDPE

Low density polythene:

• Formed under high temp and high pressure.

• The polymer is formed rapidly - molecules not neat or symmetrical, LOTS of branches

Softer and more flexible due to chains being packed less closely.

High density polythene:

• Formed under low pressure. Uses a catalyst to avoid high pressure.

• Milder conditions, less branches.

• Polymer to pack together tightly, increasing the density and the hardness of the polymer

• Stronger but less flexible due to chains being packed close

Basic addition polymerisation:

Opening up double bond so it can pair with another nonomer.

THERMOPLASTIC VS THERMOSETTING

Thermoplastic

Are polymers that can be heated again and reshaped

Hint: Plastic = moulded and shaped

This is because when heated the weak dispersion forces break

allowing chains to slide past one another, however the strong

covalent bonds still hold the chains in place.

Can often be recycled

Eg. Polyethene

Thermosetting

Cannot be remoulded. (Once they are heated their shape is

set)

Hint: Set = In place

This is because they have cross-links between chains, and

therefore stronger forces holding them together.

When sufficient energy is supplied to break this force, the

covalent bonds also break.

Eg. Saucepan handles, bowling balls and shatterproof

crockery